<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    * {
      box-sizing: border-box;
    }
    .container {
      width: 310px;
      height: 310px;
      border: 5px solid salmon;
      position: relative;
    }
    .unit {
      width: 10px;
      height: 10px;
      background-color: royalblue;
      border: 1px solid black;
      position: absolute;
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="snake"></div>
  </div>

  <script src="index.js"></script>
</body>
</html>
